POS0325 THE ASSOCIATION BETWEEN OBESITY, SOCIOECONOMIC POSITION AND KNEE JOINT REPLACEMENT SURGERY IN PATIENTS WITH OSTEOARTHRITIS: RESULTS FROM THE ENGLISH LONGITUDINAL STUDY OF AGEING
Authors: R. Witkam, S. Verstappen, J. Gwinnutt, M. Cook, T. O’neill, R. Cooper, J. Humphreys
Journal: Annals of the Rheumatic Diseases (2022)

Background Evidence suggests that associations of lower socioeconomic position (SEP) with increased incidence of osteoarthritis (OA) are partially mediated by obesity. Obesity and lower SEP are also associated with increased symptoms in OA (i.e. pain/function). However, few studies have investigated whether obesity and lower SEP are also associated with increased risk of knee joint replacement surgeries (kJRS). Objectives To investigate the relationships of obesity and SEP at time of diagnosis with kJRS at follow-up in people with knee OA (kOA). Methods The English Longitudinal Study of Ageing is a nationally representative panel study of adults aged ≥50 years with biannual waves of data collection (2002–2019). Participants who self-reported OA diagnosis for the first time in waves 2–8 and knee pain in the same or previous wave of diagnosis were defined as having kOA (baseline). Participants with at least one body mass index (BMI) measurement and one follow-up assessment were included. Underweight/normal weight, overweight and obesity were defined using BMI &lt;25 kg/m 2 , 25–30 kg/m 2 and ≥30kg/m 2 , respectively. Education, occupation (current or last occupation if retired), wealth quintiles (all individual-based) and index of multiple deprivation quintiles (area-based) were used as SEP indicators. Outcome was the first self-reported kJRS (left or right knee) in waves 3–9. Cox proportional hazards models were used to investigate the associations of obesity and SEP with kJRS, controlling for baseline covariates. Person year follow up was calculated from baseline to either a) date of self-reported kJRS, b) loss to follow-up, c) end of follow-up (wave 9). Results The analysis sample included 1499 people who reported kOA and had ≥1 BMI measure (62.3% female; mean age 66.5y (SD 9.4); 96% white; 47.4% obese). Number of person-years included in the analysis was 8427. Over a mean follow-up of 4.7 years (SD 2.8), 144 (9.6%) reported having kJRS. Obese kOA patients were more likely to report kJRS than non-obese patients (adjHR 1.89 (95% CI 1.33, 2.68)), independent of age, gender, SEP, cardiovascular disease (self-reported) and HbA1c values (measured from collected blood samples). Education and occupation were not associated with kJRS. However, those living in the most deprived areas and with the least amount of wealth were less likely to undergo kJRS compared with the least deprived and wealthiest (HRs adjusted for age and gender 0.37 (95% CI 0.19, 0.73) and 0.55 (95% CI 0.33, 0.93), respectively). There was no evidence of interactions between obesity and SEP indicators. Conclusion Obesity increased the likelihood of undergoing kJRS in kOA patients. Therefore, reducing obesity in kOA patients may help to reduce the need for kJRS. Area-deprivation and lower wealth were associated with lower likelihood of kJRS. Taken together with findings from other studies which report associations between lower SEP and worse OA symptoms, our results suggest that there may be social inequalities in the provision of kJRS in England. Table 1. The relationships between obesity at baseline and rates of knee joint replacement surgery over a mean of 4.7 (SD 2.8) years in follow-up in those with knee OA at baseline in the English Longitudinal Study of Ageing Predictors HR (95% CI) Unadjusted Adjusted for age and gender Adjusted for age, gender and SEP Adjusted for age, gender, SEP, CVD and HbA1c Obesity 1.56 (1.12, 2.17) 1.63 (1.17, 2.28) 1.77 (1.26, 2.50) 1.89 (1.33, 2.68) Non-obesity ref ref ref ref Obesity 3.53 (1.77, 7.02) 3.58 (1.80, 7.12) 4.01 (2.01, 8.03) 4.35 (2.16, 8.74) Overweight 2.91 (1.43, 5.91) 2.81 (1.38, 5.73) 2.93 (1.44, 5.98) 2.98 (1.46, 6.09) Underweight/normal weight ref ref ref ref BMI per 1 kg/m 2 increment 1.05 (1.02, 1.07) 1.05 (1.03, 1.08) 1.06 (1.04, 1.09) 1.07 (1.04, 1.10) HR, hazard ratio; CI, confidence interval; SEP, socioeconomic position; CVD, cardiovascular disease; ref, reference category; BMI, body mass index. Disclosure of Interests None declared